Switch

ABSTRACT

A loadbreak switch which can repeatedly open and close a circuit to a load for 200 operations or more at a current of 300 amperes or more and at a voltage of 13,000 volts or more. The switch includes two conductors connected from two fixed terminals. An arm is pivoted from one terminal and has a contact at its free end to engage the other terminal. The contact is mounted on the end of a shaft slidable in the arm. A vacuum interrupter is mounted in the arm in a position to be actuated and deactuated by axial movement of the shaft relative to the arm. The interrupter breaks before the contact breaks and makes after the contact makes. Since the interrupter is normally actuated and deactuated axially, the switch is uncomplicated, inexpensive, requires few parts and is compact.

United States Patent McCloud [54] SWITCH [72] Inventor:

[73} Assignee:

George Randall McCloud, San Jose, Calif.

International Telephone 'and Telegraph Corporation, New York, NY.

(22] Filed: n;c.s1,1970

[2i] Appl.No.: 103,023

[ Feb. 29, 1972 FOREIGN PATENTS OR APPLICATIONS 523,674 7/1940 GreatBritain ..200/146R Hemminger, Charles L. Johnson, Jr. and Thomas E. Kristofferson 571 ABSTRACT A loadbreak switch which can repeatedly open and close a circuit to a load for 200 operations or more at a current of 300 amperes or' more and at a voltage of l3,000 volts or more. The switch includes two conductors connected from two fixed ter- [56] References Cited minals. An arm is pivoted from one terminal and has a contact at its free end to engage the other terminal. The contact is UNITED STATES PATENTS mounted on the end of a shaft slidable in the arm. A vacuum interrupter is mounted in the arm in a position to be actuated g ls? i al and deactuated by axial movement of the shaft relative to the 2480622 8 1949 "200/I46 R arm. The interrupter breaks before the contact breaks and l makes after the contact makes. Since the interrupter is nor- 2,773,154 l2/ l956 Williams ..200/14 R mally actuated and deactuated axially, the switch is uncomi g fi g plicated, inexpensive, requires few parts and is compact. c wager 3,038,980 6/1962 Lee ..200/1 44 B 13 Claims, 4 Drawing Figures 25 9 82 t E e 1 a, F a Q a I /e 92 T W 85 I 53 4 la 97 e2 9 95 a5 a3 66 e/ as 84 2 .96 fig e0 5@ 6? l Patented Feb. 29, 1972 3 Sheets-Sheet mvsmoa GEORGE E. McCzoua BY Patented Feb. 29, 1972- 3 Sheets-Sheet .QTTORA/EV Patented Feb. 29, 1972 3,646,294

S Sheets-Sheet 5 INVENTOR. BYGEOBGE- 2 Me CLOUD SWITCH BACKGROUND OF THE INVENTION This invention relates to electrical switches having auxiliary enclosed contacts to make and break after and before, respectively, the main contacts make and break, and more particularly, to a loadbreak switch or the like.

Loadbreak switches are frequently employed in power distribution applications where the current is in the hundreds of amperes and the voltage is in the thousands of volts. It is thus very important to make such switches as a safe as possible and to make them so that they will work reliably due to the hazard to workmen in the vicinity.

In the past, it has been the practice to employ a vacuum interrupter with a main knife blade switch for a loadbreak switch. The main switch has a long arm so that the workmen can inspect its position from a considerable distance and can thereby be assured from the position of the arm that the switch is open or closed.

Notwithstanding the foregoing, it is desirable to use the vacuum interrupter to prevent the application of one line potential to one main contact and the passage of current through the main contacts during opening and closing thereof. This is true because the interrupter can break high currents at high voltage for a large number of operations whereas theair break contacts melt by the heat created by an arc therebetween and throw off molten droplets of metal.

In the prior art it is conventional to operate the interrupter switch contacts contemporaneously by a mechanism connected between the main switch arm and the interrupter. For example, see US. Pat. Nos. 2,872,550; 2,810,805; 2,773,154; 2,480,622 and 3,038,980. See also German Pat. No. 615,965.

The prior art interrupters are usually mounted in a fixed position. Due to the fact that the main switch arm is pivoted and the interrupter is actuated by a linear motion, the mechanism connecting the main switch and interrupter is normally complicated, expensive and requires a large number of component parts. Accordingly, the loadbreak switch is also usually relatively large in size. Otherwise, prior art switches do not work reliably for a large number of operations.

The above described and other advantages of the present invention will be better understood from the following detailed description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings which are to be regarded as merely illustratwe:

FIG. 1 is an exploded perspective view of a loadbreak switch constructed in accordance with the present invention;

FIG. 2 is a broken side elevational view of the switch, partly in section;

FIG. 3 is a rear end elevational view of the switch; and

FIG. 4 is a transverse sectional view of the switch taken on the line 4-4 shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a loadbreak switch is indicated at 10. Switch is supported on an insulator 11 that carries a laminated cantilever leaf spring contact 12. An upper layer 13 of contact 12 may be made of spring steel. An intermediate layer 14 thereof may be made of copper. A lower layer 15 thereof may also be made of copper. Insulator 11 also carries a yoke 16 which has metal strips 17 and 18. Yoke 16 has arms 19 and 20 through which aligned holes 21 are located.

Switch 10 also includes an arm 22 having a bracket 23 fixed to one end thereof. Bracket 23 has cars 24 and 25 with aligned holes 26 therethrough.

When assembled, contact 12 is fixed to a metal member 27 to engage a contact 28 fixed to a shaft 29 that is slidable into and out of a hollow plastic cylinder 30 of arm 22.

Also, when assembled, holes 21 and 26 are held in alignment by a bolt 31, shown in FIG. 3.

' In FIG. 1, a handle 32 is fixed to a plug 33 in cylinder 30 by Phillips head screws 34, as shown in FIG. 2.

In the operation of the switch 10 in FIG. 1, arm 22 is rotated aboutthe axis of holes 21 until contact 28 engages cam surfaces 35 and 36 of member 27. This pulls shaft 29 outwardly of cylinder 30, and maintains a pair of vacuum interrupter contacts, to be described, separated before contact 28 engages contact 12.

After arm 22 has been pivoted in between legs 37 and 38 of member 27 from a position between diverging wings 39 and 40 to a position therebetween at the location of lower cam surfaces 41 and 42, the spring action of contact 12 depresses contact 28. Shaft 29 is then moved and the vacuum interrupter contacts make.

When arm 22 is moved upwardly from the position illustrated in FIG. 2, cam surfaces 35 and 36 with spring 84 positively move contact 28 and thus break the interrupter contacts and any welds occurring thereat. Spring 84 biases the interrupter contacts toward the open position, although the spring force of contact 12 overcomes the force of spring 84 when the switch 10 is in the position shown in FIG. 2. However, spring 84 always tends to open the interrupter contacts and does so at all times during movement of the arm 22 upwardly in FIG. 2 after the interrupter contact has been moved out of engagement with contact 81. That is, during said upward movement, the interrupter contacts never remake after contact 28 no longer touches cam surfaces 35 and 36.

As arm 22 is pushed from a position completely out of tough with member 27 toward the closed position shown in FIG. 2, the interrupter contacts never make until contact 28 arrives at a position over surfaces 41 and 42.

As shown in FIG. 2, insulator 11 has smooth cylinder portions 43, 44 and 45. Contact 12 and yoke 16 are fixed relative to surfaces 43 and 45, respectively, by substantially identical means. Similarly, a supporting bracket 46 is fixed relative to surface 44 by substantially the same said means.

Bracket 46 has a hole 47 therethrough for a bolt connection or the like. A strap 48 is held in tension around surface 44 by a hook connection with a block 49. A set screw 50 is slidable through a hole 51 in bracket 46 and is threaded through block 49. A block 52 distributes the stress on the insulator 11 created by turning screw 50 down.

At the ends of the insulator l l, straps 53 and 54 may be substantially identical to strap 48. Blocks 55 and 56 may be substantially identical to block 52. Blocks 57 and 58 may be substantially identical to block 49. However, blocks 57 and 58 have holes 59 and 60 therethrough through which pins 61 and 62 are press fit. Pins 61 and 62 are also press fit through corresponding holes in all of the structures surrounding them.

The mounting means at the right end of the switch 10, as shown in FIG. 2, has a bracket 63 with a hole 64 therethrough for connection to an electrical lead. The means at the right end of FIG. 2 also includes a mounting plate 65. The means are held together by a screw 66. Screw 66 is slidable through corresponding holes in plate 65, members 17 and 18 and bracket 63, screw 66 being threaded only through block 58.

As shown in FIG. 3 and FIG. 4, block 58 has projections 67 and 68. Strap 54 has hooks 69 and 70 which fit over projections 67 and 68. See also the similar construction of block 49 and strap 48 in FIG. 3. Block 57 and strap 53 also have the same construction but are oriented the same as block 58 and strap 54 in FIG. 3.

A spool 71 is located around the shank 72 of bolt 31, shown in FIGS. 2 and 3.

As shown in FIG. 2, an entirely conventional vacuum interrupter 73 is located concentrically within cylinder 30. Interrupter 73 includes an evacuated envelope 74. Envelope 74 comprises two ceramic cylinders 75 and 76 brazed together and metal end seals 77 and 78 brazed thereto, respectively. Interrupter 73 also includes two conductive shafts 79 and 80 having contacts 80 and 81, respectively, which may be brought into engagement with each other, and pulled apart so that the contacts 80 and 81 do not touch each other.

Shaft 79 is brazed to end cap 77. The left end of a bellows 81, as shown in FIG. 2, is brazed to shaft 80. The right end of bellows 81 is brazed to end cap 78. The interior of bellows 81 is thus at atmospheric pressure. The construction of interrupter 73 inside envelope 74 may be entirely conventional.

Bracket 23 has a central flange 82 through which shaft 80 projects. Flange 82 is clamped to shaft 80 by conventional clamp means 83.

A helically coiled spring 84 is positioned between bracket 23 and endcap 78. The purpose of spring 84 is to ensure that contacts 80 and 81 are held apart except when pressed together by the force exerted by contact 12 against member 28.

Shaft 79 is pinned to shaft 29 at 85. l

A web 86 is fixed inside cylinder 30 by a pin 87. Shaft 29 is slidable through web 86. Note will be taken that pin 85 projects beyond the outer cylindrical surface of shaft 29. Thus, with arm 22 rotated upwardly, as viewed in FIG. 2, any force on shaft 29 tending to separate contacts 80 and 81 beyond a desiredlimit may be prevented by engagement of pin 85 with web 86.

Note will'be made that, in FIG. 2, handle 32 has a portion 88 with a hole therethrough in registration with a corresponding hole through insert 33. Thus, shaft 79 slides through both of the holes in portion 88 and insert 33.

Contact 28 terminates in a hollow conductive cylinder 90, as shown in FIG. 2, which is pinned to cylinder 29 at 91.

Portions 37 and 38 of member 27 are held in fixed positions relative to each other by their integral connection, and also by a bolt 92 which extends therethrough and clamps them together against a resilient spacer 93 serving as a stop to the inward motion of switch 10.

Member 27 has a transverse portion 95, shown in FIGS. 1 and 2, which is fixed to a bracket 96 by screws 97 and 98. Bracket 96, in turn, is fixed relative to insulator 11 by being clamped by screw 99 between contact 12 and block 57.

The laminations of contact 12 are held together by a rivet 100.

Contact 12 has a hole 101 therethrough so that an electrical lead may be connected to the contact 12.

In the view of the loadbreak switch of the present invention shown in FIG. 2, contacts 80 and 81 are closed. Contacts 12 and 28 touch each other.

To open the switch of FIG. 2, arm 22 is raised upwardly, as viewed in FIG. 2. Cam surfaces 35 and 36 are shaped and located so that contact 28 will be lifted an amount sufficient to break contacts 80 and 81 before contact 28 separates from contact 12 even though contacts 80 and 81 may resist separation as the result of slight welding.

Conversely, when the switch is closed, arm 22 is rotated so that contact 28 approaches contact 12. As arm 22 is moved still further from the peak positions of cam surfaces 35 and 36 to a position over portions 41 and 42 thereof, as shown in FIG. 2, the force of the spring of contact 12 will cause shaft 29 to be moved with contact so that contacts 80 and 81 will make.

Note will be taken that the contacts and many other component parts of the present invention may be made separate from or integral with the shafts or other parts without departing from the true scope of the invention.

Note will also be taken that the shaft 80 of interrupter 73 may be connected to shaft 29, and that shaft 59 may be clamped in flange 22 without departing from the invention. In this case, spring 84 may be located between end cap 78 and web ,86.

From the foregoing, it will be appreciated that vacuum interrupters of the conventional type shown at 73 are axially operated. Thus, the loadbreak switch 10 of the present invention ideally operates interrupter 73 by a single axial motion of contact 28produced by contact 12, or by the combination of contact 12 with member 27.

What is claimed is:

l. A switch comprising: support means; an arm having one end pivoted on said support means; a first contact fixed relative to said support means; a second contact; an auxiliary switch mounted on said arm, said auxiliary switch having third and fourth contacts, said third contact being movable into and out of engagement with said fourth contact; and movable operating means including conductive means connecting said second and third contacts, said operating means being responsive to movement of said second contact during engagement thereof with said first contact to cause engagement of said third contact with said fourth contact after initial engagement of said second contact with said first contact, said second contact being fixed relative to, and carried by, said operating means in a position to engage said first contact when said arm is rotated about it pivot to a corresponding position, said first contact and said pivot being spaced apart.

2. The invention as defined in claim 1, wherein said auxiliary switch is a vacuum interrupter having first and second conductive shafts, each shaft having one end adapted to abut that of the other, said shafts being located on a common axis, a sealed evacuated envelope for said shafts, said first shaft being sealed through said envelope, a bellows sealing and second shaft to said envelope at a point intermediate the ends of said second shaft, means to mount the other end of one shaft in a fixed position relative to said arm, said operating means including means connected between the other shaft and said second contact.

3. The invention as defined in claim 2, including guide means fixed relative to said support means, said guide means including a first cam having a cam surface, a projection fixed relative to saidsecond contact to ride on said cam surface, said cam surface being located on the side of said cam opposite to that which extends toward the pivot axis of said arm, said cam surface having a shape and location such that said projection and operating means are moved away from said pivot axis and said third and fourth contacts are disengaged before said second contact touches said first contact, said first cam having a construction and location such that said first and second contacts are insulated from each other except when said second contact touches said first contact.

4. The invention as defined in claim 3, including a second cam substantially identical to said first cam, each of said cams being substantially planar, said cam surfaces being substantially perpendicular to the cam planes, said planes converging toward said first contact, said cam planes being normal to a common plane, said arm including a dielectric cylinder, said operating means including a shaft concentric with said cylinder and slidable axially therein, said second contact being fixed to said concentric shaft, said second contact having a disc concentric with. said shaft, said shaft having a diameter smaller than the spacing of said cams, said disc having a diameter larger than the spacing of said cams.

5. The invention as defined in claim 2, including spring means mounted on said arm to urge said envelope in a direction away from the other end of said second shaft to hold said third and fourth contacts apart when said second contact is disengaged from said first contact.

6. A switch comprising: support means; first and second conductors fixed relative to said support means; an arm having a hollow, cylindrical shell; a first bracket fixed relative to said shell at one end thereof; a second bracket fixed to said second conductor; means to hinge said brackets together so that said arm will pivot about an axis perpendicular to that of said shell; a vacuum interrupter including a sealed evacuated envelope, a first conductive shaft sealed through said envelope, a second conductive shaft, and a collapsible bellows sealing said second shaft to said envelope intermediate said second shaft ends, said interrupter shafts being located concentric with said shell and internally thereof, said second interrupter shaft being movable relative to said first shaft and said envelope, and vice versa, by collapsing said bellows, said first and second shafts being movable from relative positions with their mutually adjacent ends abutting to relative positions with said adjacent ends out of contact with each other; means to hold the nonadjacent end of one of said first and second shafts in a fixed position relative to said arm, said one shaft extending out of said envelope toward said hinge; an annular body fixed relative to said shell, said body having a hole therethrough with a cylindrical surface concentric with that of said shell; a third shaft fixed to the nonadjacent end of the other of said first and second shafts, said third shaft being slidable axially through said body and extending therethrough and through said arm and said shell to a position beyond the other end of said arm and said shell; a first contact member fixed relative to said third shaft at the end thereof outside said arm and said shell; a second contact fixed relative to said first conductor, said second contact extending generally in the plane of hinged movement of said arm toward, said second contact having one surface portion approximately perpendicular to said shell axis when said contact members engage each other and another surface located at an acute angle relative to said one surface contiguous thereto to cause said third shaft to be pushed axially into said shell when said arm is rotated to bring said first contact member from in contact with said other surface portion to a location in contact with said one surface portion.

7. The invention as defined in claim 6, including guide means fixed relative to said support means, said guide means including a first cam having a cam surface, a projection fixed relative to said second contact member to ride on said cam surface, said cam surface being located on the side of said cam opposite to that which extends toward the pivot axis of said arm, said cam surface having a shape and location such that said projection and third shaft are moved away from said pivot axis and said first and second shafts are disengaged before said first contact member touches said second contact 'member, said first cam having a construction and location such that said first and second contact members are insulated from each other except when said first contact member touches said second contact member.

8. The invention as defined in claim 7, including a second cam substantially identical to said first cam, each of said cams being substantially planar, said cam surfaces being substantially perpendicular to the cam planes, said planes converging toward said first contact, said cam planes being normal to a common plane, said first contact member having a disc concentric with said third shaft, said third shaft having a diameter smaller than the spacing of said cams, said disc having a diameter larger than the spacing of said cams.

9. The invention as defined in claim 6, including spring means mounted on said arm to urge said envelope in a direction away from the other end of said second shaft to hold said first and second shafts apart when said first contact member is disengaged from said second contact member.

10. The invention as defined in claim 9, wherein said spring means is an open coil helical spring located between said envelope and said first bracket with the helix axis being the same as that of said shell.

11. The invention as defined in claim 6, wherein both of said brackets are made of an electrically conductive material. said one of said first and second shafts being electrically connected to said second conductor through both of said brackets, said first contact member and said third shaft both being made of a conductive material, said first contact member being electrically connected to said other shaft through said third shaft, said first and second shafts being insulated from each other except when they abut one another.

12. The invention as defined in claim 6, including a web fixed to said shell inside thereof between said body and said envelope, said other of said first and second shaftsbeing a solid conductive metal cylinder, said third shaft being a hollow conductive metal cylinder telescoped over said other shaft, a pin press fit through both of said other and said third shafts at a location between said web and said envelope, said web having a hole therethrough with a cylindrical surface concentric with that of said shell, said third shaft being slidable through said web hole, said pin projecting radially beyond said third shaft to engage said web on movement of said third shaft outward] of said shell and to act as a stop for said third shaft.

3. e invention as defined in claim 6, wherein said second contact member is a cantilever leaf spring fixed at the end thereof nearest said one surface portion relative to said first conductor. 

1. A switch comprising: support means; an arm having one end pivoted on said support means; a first contact fixed relative to said support means; a second contact; an auxiliary switch mounted on said arm, said auxiliary switch having third and fourth contacts, said third contact being movable into and out of engagement with said fourth contact; and movable operating means including conductive means connecting said second and third contacts, said operating means being responsive to movement of said second contact during engagement thereof with said first contact to cause engagement of said third contact with said fourth contact after initial engagement of said second contact with said first contact, said second contact being fixed relative to, and carried by, said operating means in a position to engage said first contact when said arm is rotated about it pivot to a corresponding position, said first contact and said pivot being spaced apart.
 2. The invention as defined in claim 1, wherein said auxiliary switch is a vacuum interrupter having first and second conductive shafts, each shaft having one end adapted to abut that of the other, said shafts being located on a common axis, a sealed evacuated envelope for said shafts, said first shaft being sealed through said envelope, a bellows sealing and second shaft to said envelope at a point intermediate the ends of said second shaft, means to mount the other end of one shaft in a fixed position relative to said arm, said operating means including means connected between the other shaft and said second contact.
 3. The invention as defined in claim 2, including guide means fixed relative to said support means, said guide means including a first cam having a cam surface, a projection fixed relative to said second contact to ride on said cam surface, said cam surface being located on the side of said cam opposite to that which extends toward the pivot axis of said arm, said cam surface having a shape and location such that said projection and operating means are moved away from said pivot axis and said third and fourth contacts are disengaged before said second contact touches said first contact, said first cam having a construction and location such that said first and second contacts are insulated from each other except when said second contact touches said first contact.
 4. The invention as defined in claim 3, including a second cam substantially identical to said first cam, each of said cams being substantially planar, said cam surfaces beIng substantially perpendicular to the cam planes, said planes converging toward said first contact, said cam planes being normal to a common plane, said arm including a dielectric cylinder, said operating means including a shaft concentric with said cylinder and slidable axially therein, said second contact being fixed to said concentric shaft, said second contact having a disc concentric with said shaft, said shaft having a diameter smaller than the spacing of said cams, said disc having a diameter larger than the spacing of said cams.
 5. The invention as defined in claim 2, including spring means mounted on said arm to urge said envelope in a direction away from the other end of said second shaft to hold said third and fourth contacts apart when said second contact is disengaged from said first contact.
 6. A switch comprising: support means; first and second conductors fixed relative to said support means; an arm having a hollow, cylindrical shell; a first bracket fixed relative to said shell at one end thereof; a second bracket fixed to said second conductor; means to hinge said brackets together so that said arm will pivot about an axis perpendicular to that of said shell; a vacuum interrupter including a sealed evacuated envelope, a first conductive shaft sealed through said envelope, a second conductive shaft, and a collapsible bellows sealing said second shaft to said envelope intermediate said second shaft ends, said interrupter shafts being located concentric with said shell and internally thereof, said second interrupter shaft being movable relative to said first shaft and said envelope, and vice versa, by collapsing said bellows, said first and second shafts being movable from relative positions with their mutually adjacent ends abutting to relative positions with said adjacent ends out of contact with each other; means to hold the nonadjacent end of one of said first and second shafts in a fixed position relative to said arm, said one shaft extending out of said envelope toward said hinge; an annular body fixed relative to said shell, said body having a hole therethrough with a cylindrical surface concentric with that of said shell; a third shaft fixed to the nonadjacent end of the other of said first and second shafts, said third shaft being slidable axially through said body and extending therethrough and through said arm and said shell to a position beyond the other end of said arm and said shell; a first contact member fixed relative to said third shaft at the end thereof outside said arm and said shell; a second contact fixed relative to said first conductor, said second contact extending generally in the plane of hinged movement of said arm toward, said second contact having one surface portion approximately perpendicular to said shell axis when said contact members engage each other and another surface located at an acute angle relative to said one surface contiguous thereto to cause said third shaft to be pushed axially into said shell when said arm is rotated to bring said first contact member from in contact with said other surface portion to a location in contact with said one surface portion.
 7. The invention as defined in claim 6, including guide means fixed relative to said support means, said guide means including a first cam having a cam surface, a projection fixed relative to said second contact member to ride on said cam surface, said cam surface being located on the side of said cam opposite to that which extends toward the pivot axis of said arm, said cam surface having a shape and location such that said projection and third shaft are moved away from said pivot axis and said first and second shafts are disengaged before said first contact member touches said second contact member, said first cam having a construction and location such that said first and second contact members are insulated from each other except when said first contact member touches said second contact member.
 8. The invention as defined in claim 7, including a second cam substantially identical to said first cam, each of said cams being substantially planar, said cam surfaces being substantially perpendicular to the cam planes, said planes converging toward said first contact, said cam planes being normal to a common plane, said first contact member having a disc concentric with said third shaft, said third shaft having a diameter smaller than the spacing of said cams, said disc having a diameter larger than the spacing of said cams.
 9. The invention as defined in claim 6, including spring means mounted on said arm to urge said envelope in a direction away from the other end of said second shaft to hold said first and second shafts apart when said first contact member is disengaged from said second contact member.
 10. The invention as defined in claim 9, wherein said spring means is an open coil helical spring located between said envelope and said first bracket with the helix axis being the same as that of said shell.
 11. The invention as defined in claim 6, wherein both of said brackets are made of an electrically conductive material, said one of said first and second shafts being electrically connected to said second conductor through both of said brackets, said first contact member and said third shaft both being made of a conductive material, said first contact member being electrically connected to said other shaft through said third shaft, said first and second shafts being insulated from each other except when they abut one another.
 12. The invention as defined in claim 6, including a web fixed to said shell inside thereof between said body and said envelope, said other of said first and second shafts being a solid conductive metal cylinder, said third shaft being a hollow conductive metal cylinder telescoped over said other shaft, a pin press fit through both of said other and said third shafts at a location between said web and said envelope, said web having a hole therethrough with a cylindrical surface concentric with that of said shell, said third shaft being slidable through said web hole, said pin projecting radially beyond said third shaft to engage said web on movement of said third shaft outwardly of said shell and to act as a stop for said third shaft.
 13. The invention as defined in claim 6, wherein said second contact member is a cantilever leaf spring fixed at the end thereof nearest said one surface portion relative to said first conductor. 